144 



Ellen C. Weaver and Norman I. Bishop 



o 

 o 



in 

 < 



UJ 



o 



LIGHT OFF 



NO.II- 



NO. II 525 m^ {50 RUNS) 



TOTAL PERIOD 

 4 SECONDS 



0.5 sec 



LIGHT 

 ON 



LIGHT 

 OFF 



Fig. 6 Time course of alDsorption changes with a 0.5 second flash 



at 525 m|j, in wild type and an "O2" mutant (No. 11). The 

 two phase rise in wild type is contrasted with the negative shift 

 in the same preparation at 425 i^M- which remains approximately ex- 

 ponential. Note the decay during the 0.5 second flash in No. 11. 



entirely in the dark period, thus accounting for the greater 

 initial increase in absorption observed with the shorter flash 

 (Fig. 7). 



The time course behavior of No. 8, wild type, and No. 11 com- 

 pose a series of increasing complexity. These were suspended in 

 water without added substrate. However, addition of benzoquinone 

 to No. 8, while allowing it to evolve oxygen, does not perceptib- 

 ly change its optical behavior. Nor does saturating No. 11 with 

 hydrogen gas, which it can use for the photoreduction of carbon- 

 ate, change the characteristics displayed here. However, it has 

 been shown that adapting wild type Scenedesmus to hydrogen over a 

 number of hours enables it to carry out anaerobic photoreduction. 



